The expected point source detection sensitivity depends both on exposure
and background behavior. A detailed discussion of
the expected ROSAT PSPC background is given in § 7.8.2 of
this document. Figure 6.2 shows the calculated mean minimum
detectable count rate from point sources and its variance as a function
of ecliptic latitude. The increase in sensitivity towards the poles of
the ecliptic can be noticed. Also it follows from Figure 6.2
that the least sensitive portions of the all-sky survey will be located at
southern mid-latitudes.